Method of disinfecting and self-limiting solution therefor

ABSTRACT

A SOLUTION CONTAINING AN INORGANIC HYPOCHLORITE SALT AND AN INORGANIC SALT OF A HYDROXY CARBOXYLIC ACID AND OPTIONALLY CONTAINING AN ACID TO ADJUST THE PH TO 4.5-8 AND/OR A DETERGENT, WHICH DISINFECTS SENSITVE MATERIALS WITHOUT HARMING THE MATERIAL BY REMAINING ACTIVE FOR A SHORT PEROID OF TIME DUE TO SELF CONSUMMATION FEATURE OF THE SOLUTION.

Feb. 20, 1973 w, Ec ETAL 3,717,580

METHOD OF DISINFECTING AND SELF'LIMITING SOLUTION THEREFOR Filed Dec. 2,1969 Ioo 0 PERCENT I PERCENT HYPOCHLORITE HYPOCHLORITE REMAINING REACTEDI I l l l I l I I l I I I 998 O 0 2 4 6 8 I0 I2 14 REACTION TIMEIMINuTEsI William H. Echols INITIAL CONCENTRATIONS George FiddingSOLUTION HYPOCHLORITE CITRATE Rex A Neihof B 0.0l5 M 0.007M INVEXTORS c0.02l 0 0.035 E 0.063 F 0.09l H 0.I05

% o ATTURIQ- Y United States Patent US. Cl. 252-106 9 Claims ABSTRACT OFTHE DISCLOSURE A solution containing an inorganic hypochlorite salt andan inorganic salt of a hydroxy carboxylic acid and optionally containingan acid to adjust the pH to 4.5-8 and/or a detergent, which disinfectssensitive materials without harming the material by remaining active fora short period of time due to a self consummation feature of thesolution.

BACKGROUND OF THE INVENTION This invention generally relates to the artof disinfecting and more particularly to disinfecting with an aqueoushypochlorite solution which retains its germicidal activity for arelatively short time.

Hypochlorite' solutions have been used for many years asgermicides,sporicides, virucides and chemical warfare decontaminarits'.However, their prior use has been generally limited'to terrain, heavyconstruction materials and other items resistant to the inherentcorrositivity of hypochlorites. When used on more sensitive materialssuch as clothing fabrics, one or very few applications could betolerated. The human body has always been considered too sensitive amaterial for routine or repeated disinfection or decontamination byhypochlorite solution. Thus, when it was desired to disinfect ordecontaminatehypochlorite sensitive materials it has been necessary touse less powerful disinfection or decontamination agents therebyreducing the effectiveness thereof.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is toprovide a method of disinfecting or decontaminating sensitive materialsusing a new aqueous hypochlorite containing composition.

Another object of this invention is to provide a new aqueoushypochlorite containing disinfectant solution.

A still further object of this invention is to provide hypochloritecontaining solutions which remain germicidally active for a short periodof time.

Andther object of this invention is to provide hypochlorite containingsolutions which self-destruct.

These and other objects of this invention are accomplished by providingan aqueous disinfectant solution containing an inorganic hypochloritesalt and an inorganic salt of a hydroxy carboxylic acid.

BRIEF DESCRIPTION OF THE DRAWING Other objects and many of the attendantfeatures of the present invention will be readily appreciated as thesame becomes better understood by reference to the solitary drawingwhich is a graphical illustration of the percent hypochlorite remainingunreacted as the time increases for six different solutions containingvarying amount of citrate ion.

DESCRIPTION OF THE PREFERRED EMBODIMENT The disinfecting solution ofthis invention comprises an inorganic hypochlorite salt and an inorganicsalt of a hydroxy carboXylic acid and can optionally contain some acidto adjust the pH and/or a detergent or detergent mixture.

To obtain reasonably good disinfection the inorganic hypochlorite saltshould be present in the solution in an amount sufficient to give ahypochlorite ion concentration of at least about 0.015 M and, for mostuses, a concentration of 0.015 M is sufiicient although higherconcentration may be used if desired. The preferred salts are sodium,calcium and lithium because these are the most readily availableinorganic hypochlorite salts. However, any inorganic hypochlorite may beused without affecting the disinfectant qualities of this solution sinceit is generally known that the hypochlorite ion is the source of theactive disinfecting agent and not the cation.

It is preferable, but not necessary, to also add a detergent ordetergent mixture to the disinfecting solution for the purpose ofenhancing wetting. Any anionic or non-ionic surfactant may be used forthis purpose but one should not use cationic surfactants. Generally, thedc tergent may be present in about 0.05% by weight but, in any event,the amount used is not critical.

Additionally, an acid is preferably added to the solu-= tion in order toadjust the pH to a value of between 6.5 and 7.5. The commerciallyavailable hypochlorite solutions are quite alkaline having a pH of about10.-5-11. It is generally believed that hypochlorous acid is thegermicidal component in all hypochlorite solutions, but it is present inonly very small amounts at high pH values. At a pH of about 7, however,about three-fourths of the hypochlorite is present as hypochlorous acidand only about one-fourth'as hypochlorite ion. To be more specific, forthe same amount of total available chlorine, the concentration ofhypochlorous acid has been found to be about 3,000 times as large at pH7 as at pH 10.5. Thus, the alkaline hypochlorite solution can beactivated by the addition of any acid which is stronger thanhypochlorous acid, such as citric acid or sodium dihydrogen phosphate.Thus, while good germicidal activity is attained between pH 4.5 and 8the optimum pH is 6.5 to 7.5. Table I is a compilation of the relativeconcentrations of hypochlorus acid and hypochlorite ion in water at 25C. at various pH values based on Ka=4.0 10

For the purpose of retaining the most desirable pH of 6.5 to 7.5 weakacids are preferred since in addition to acidifying the solution theyalso act as buffers to keep the pH near a magnitude of 7.

The inorganic salt of the hydroxy carboxylic acid is the constituent inthe solution of this invention which brings about the self-limitingcharacter of the solution. Since the hypochlorite will oxidize thisconstituent and very little reaction is present during the first fewseconds of contact it is possible for the hypochlorite to disinfect fora short period of time and then to be neutralized in situ. Although anyinorganic salt of hydroxy containing carboxylic acids will Work theinorganic salts of citric acid (e.g. sodium citrate) and malic acid havebeen found preferable. Thus, when a solution contains 0.015 Mhypochlorite ion and 0.007 M citrate ion the half-life is about minutes.The solitary drawing shows a number of curves indicating the half-livesof a number of solutions which have varying concentrations of citrateion. In order for the solutions of this invention to be practicallyuseful, it is desirable that the half-life not exceed 10 minutes so theratio of hypochlorite concentration to citrate ion concentration willbe, at most, about 2:1. It will be obvious to one Skilled in the artthat as the half-life is decreased the citrate ion concentration goes upand the ratio becomes smaller, e.g. 1:1 or 113 etc.

Typical formulations by weight of a self-limiting hypochlorite solutionare as follows:

. Percent Calcium hypochlorite 0.2 Triton X-100 (Rohm and Haas)(non-ionic detergent) 0.05 Sodium citrate 1 Acid:

Citric 0.2 Or NaH PO 0.5

Since the above solutions will rapidly lose their disinfectantproperties it is generally desirable to add the hypochlorite solution tothe solution containing the inorganic salt of a hydroxy carboxylic acideither alone or with a detergent and/or an acid immediately before use.This may be achieved by merely mixing the two solutions or by sprayingwhereby two streams, one containing the hypochlorite and the othercontaining the salt of the hydroxy carboxylic acid are mixed in thenozzle of the sprayer.

The solutions of this invention have been used to simultaneouslydecontaminate a man and all items of this clothing which werecontaminated with spores of Bacillus subtilis var. niger, considered tobe equal in decontamination resistance to spores of the extremelyresistant anthrax bacillus. Thus, the shirt, trousers, hood, socks,shoes, underwear, mask and the man, himself, were decontaminated byspraying the fully clothed man. The various clothing items were assayedfor residual spores by agitating with an extraction solution in plasticbags. Shoes and mask were sectioned after decontamination and the partsseparately assayed to determine whether some areas of these items wereespecially difficult to decontaminate. Sampling of the mans skin forresidual contamination was done by ultrasonic agitation of a reservoirof extraction solution in contact with the skin. The results showed aneffectiveness of 99.9% or better on all items. Additionally, an AM-FMtransistor radio, a typewriter, an electric drill and other materialswere also decontaminated using the above solution. These materials stillfunctioned properly after decontamination and showed no ill effects fromcontact with the hypochlorite solution.

What is claimed is:

1. A method of disinfecting relatively sensitive articles comprisingcontacting said articles with a solution formed by mixing immediatelybefore use an aqueous solution of an inorganic hypochlorite salt and anaqueous solution of an inorganic salt of a hydroxycarboxylic acidselected from the group citric acid and malic acid, wherein the molarratio of said hypochlorite salt to said hydroxycarboxylic acid salt isat most 2: 1.

2. The method of claim 1 wherein the mixed solution additionallycontains an acid to adjust the pH to 4.5-8.

3. The method of claim 2 wherein the mixed solution additionallycontains a nonionic or anionic detergent.

4. The method of claim 3 wherein said inorganic hypochlorite is selectedfrom the group consisting of sodium hypochlorite, calcium hypochloriteand lithium hypochlorite.

5. The method of claim 4 wherein said inorganic hypochlorite salt iscalcium hypochlorite.

6. The method of claim 4 wherein said inorganic salt of a hydroxycarboxylic acid is an inorganic salt of citric acid.

7. The method of claim 3 wherein said inorganic salt of a hydroxycarboxylic acid is an inorganic salt of citric acid.

8. The method of claim 7 wherein said inorganic salt of a hydroxycarboxylic acid is sodium citrate.

9. The method of claim 8 wherein said acid to adjust the pH to 45-8 isNaH PO References Cited UNITED STATES PATENTS 1,732,230 10/1929 Hershman252187 2,071,091 2/1937 Taylor 424-149 2,121,501 6/1938 Hershman 4241492,199,936 5/1940 Kauffmann 252187 X 2,422,255 6/ 1947 Peters 252106 X2,993,745 7/1961 Dorsett 8-108 3,359,207 12/1967 Kaneko et al. 252993,360,470 12/ 1967 Wixon 25299 2,210,133 8/1940 Sharma 99-168 3,345,30310/1967 Schmid et al. 252186 LEON D. ROSDOL, Primary Examiner P. E.WILLIS, Assistant Examiner US. Cl. X.R..

